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Thread: strange (Petzval?) lens id

  1. #1

    Join Date
    Nov 2007
    Posts
    190

    strange (Petzval?) lens id

    Hello,

    please help with the ID of following lens -

    Click image for larger version. 

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Size:	73.1 KB 
ID:	156986 Click image for larger version. 

Name:	IMG_6548.jpg 
Views:	31 
Size:	50.1 KB 
ID:	156987 Click image for larger version. 

Name:	IMG_6549.jpg 
Views:	31 
Size:	93.9 KB 
ID:	156988 Click image for larger version. 

Name:	IMG_6553.jpg 
Views:	26 
Size:	96.7 KB 
ID:	156989

    At first it looks like a Petzval, but the front element is not cemented and is much smaller than the rear, which is air separated and a quality build.
    So, the question is - what is it ? A cheap (or early, or both) Petzval where the front group just was not glued ? Or some transition from a verres combines to Petzval ? Or something else
    A manufacturer id would be also nice.

    br,
    rado

  2. #2

    Join Date
    Nov 2007
    Posts
    190

    Re: strange (Petzval?) lens id

    measured FL is 220mm, it is F5 and pretty sharp. A sample can be seen here

  3. #3

    Join Date
    Nov 2007
    Posts
    190

    Re: strange (Petzval?) lens id

    forgot to mention that it is most probably french.
    would appreciate any input !

  4. #4

    Join Date
    Jan 2009
    Location
    Denmark
    Posts
    5,885

    Re: strange (Petzval?) lens id

    I didn't reply earlier, as it would only be guesswork. Still is!

    Must be a Petzval. The early designs often had much larger rear lens pairs compared with the front achromat. Screw tgether rear pairs is a more complex engineering job than the more usual lens/spacer/lens/retaining ring.

    Air spaced achromats were still popular as objective lenses for telescopes in the middle 19th century, although having 3 thin tin spacers. These may have been lost in connection with cleaning out the inner surfaces during the last century. You might try a paper spacer solution to avoid damage at the glass/glass contact.

    The heavy reduction section holding the front achromat looks like it is a from a limited brass casting exercise. There are obvious casting imperfections, which would have been solved in a production run.

    One way of confirming origin would be to examine the separate lenses and find out their refractive indices! There is a formula which from surface radii and focal lengths, gives refractive index of the glass. The differences between french and english glass are well known.

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